1766386 - Consider changing the default scroll snap proximity threshold

Status: RESOLVED FIXED

(Core :: Layout: Scrolling and Overflow, enhancement, P3)

Description

[Hiroyuki Ikezoe (:hiro)]

We've been using 200px in CSS units for a while.

A wpt is supposed to work with the values in between 2px and 110px.

Comment 1

[Hiroyuki Ikezoe (:hiro)]

It looks like the Chrome's threshold isn't a fixed value, it's 1/3 of scrollport?

Comment 2

[Hiroyuki Ikezoe (:hiro)]

And it looks like Webkit threshold isn't a fixed value, it's 0.3 of the scrollport.

Comment 3

[Hiroyuki Ikezoe (:hiro)]

Attachment: Bug 1766386 - Make scroll snap proximity threshold based on the snapport size rather than using a fixed preference value. r?dlrobertson

Now the threshold is 0.3*snapport size, it's mostly same as WebKit [1].
A difference is WebKit's threshold is based on the scrollport size. Given that
if scroll-padding was specified due to a position: fixed element or some
such, using snapport size (i.e. offsetted by the scroll-padding) is more
reasonable than using scrollport size.

[1] https://searchfox.org/wubkat/rev/d1911bf073cc55fc8ca76bcee8b4783539e43c2e/Source/WebCore/page/scrolling/ScrollSnapOffsetsInfo.cpp#207-208

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/bdeed1276a35
Make scroll snap proximity threshold based on the snapport size rather than using a fixed preference value. r=dlrobertson

Comment 5

[Cristian Tuns]

Backed out for causing mochitest failures in helper_scroll_snap_resnap_after_async_scroll.html

• Backout link
• Push with failures
• Failure Log
• Failure line: TEST-UNEXPECTED-FAIL | gfx/layers/apz/test/mochitest/test_group_scroll_snap.html | helper_scroll_snap_resnap_after_async_scroll.html | snap to 200px - got 468, expected 200

Comment 6

[Hiroyuki Ikezoe (:hiro)]

I was misunderstanding that this scrollDelta value for promiseMoveMouseAndScrollWheelOver means that promiseMoveMouseAndScrollWheelOver scrolls the given delta, but it's just used for creating OS internal events so it's hard to predict how far promiseMoveMouseAndScrollWheelOver scrolls to.

I did tweak the scroll delta depending on platforms to make the test pass on all desktop platforms and android.

Comment 7

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/a5bcd3edffd7
Make scroll snap proximity threshold based on the snapport size rather than using a fixed preference value. r=dlrobertson

Comment 8

[Iulian Moraru]

https://hg.mozilla.org/mozilla-central/rev/a5bcd3edffd7